Heat transfer in rough-wall turbulent thermal convection in the ultimate regime

Abstract

Heat and momentum transfer in wall-bounded turbulent flow, coupled with the effects of wall roughness, is one of the outstanding questions in turbulence research. In the standard Rayleigh-Bénard problem for natural thermal convection, it is notoriously difficult to reach the so-called ultimate regime in which the near-wall boundary layers are turbulent. Following the analyses proposed by Kraichnan [Phys. Fluids 5, 1374 (1962)] and Grossmann and Lohse [Phys. Fluids 23, 045108 (2011)], we instead utilize recent direct numerical simulations of forced convection over a rough wall in a minimal channel [MacDonald et al., J. Fluid Mech. 861, 138 (2019)] to directly study these turbulent boundary la..